In general, the output shaft of an engine is typically connected to an input shaft of a torque converter and an output shaft of a torque converter is typically connected to an input shaft of a transmission. A retarder is typically located between an input shaft of a transmission and an output shaft of a torque converter so as to provide a rotatable connection. An electronic control system is typically utilized to smoothly engage and disengage the fluid actuated retarder. The retarder functions to provide braking torque that typically results in a decrease in machine speed.
One known arrangement utilizes an on/off solenoid to engage and disengage the retarder. This on/off solenoid provides a very abrupt change in the level of retarding. This results in the retarder not being responsive to excessive machine deceleration rates. In addition, the retarder is not responsive to heat buildup in either the retarder or the transmission in order to modify the retarding level. Furthermore, this on/off application of a fixed retarding level has been known to aggravate transmission downshifting by adding excessive braking torque during the shifting operation. This prevents smooth transmission operation during downshifting. In addition, this arrangement is slow to build retarding torque.
The present invention is directed to overcoming one or more of the problems set forth above.